Private cellular telephone system

This application is a continuation of 08/111,775 filed Aug. 25, 1993, abandoned, which is a continuation of 07/962,011 filed Oct. 15, 1992, abandoned, which is a continuation of 07/831,628 filed Feb. 6, 1992, abandoned which is a continution of 07/517,923 filed May 2, 1990, abandoned.

This invention is generally related to the field of cellular telephones. The invention provides a means for connecting mobile or subscriber cellular telephones to wire lines without complex digital switches in situations in which full cellular service is inappropriate or unavailable.

In a cellular telephone system, a "subscriber" or "mobile" radiotelephone terminal unit, which may be an automobile-based, portable, or hand-held transceiver, having no fixed location communicates with a fixed, "base" radiotelephone station that is located in and acts as a communications "hub" for a particular and generally exclusive geographic region known as a "cell." Once communication is established between a given mobile terminal and base station and the mobile terminal is moved into another cell, communications with the terminal is "handed off" from the first base station to the base station for the second cell. Typically the base station is linked to a conventional local telephone trunk so that the mobile user can communicate with a conventional "wire line" (which itself may include radio transmission) telephone user from his mobile terminal.

The past decade has seen the rise of cellular telephones operating under protocols such as "AMPS" (Advanced Mobile Phone Service) or "TACS" (Total Access Communications System), respectively specified in the EIA Interim Standards IS-3-D, IS-19-A, and IS-20-A and in the United Kingdom Total Access Communications System: Mobile Station-Land Station Compatibility Specification. Generally, the implementation of these cellular telephone protocols allow two-way, fully duplexed communication between mobile terminals and base stations, each connected to a wire line, serving a limited geographic area and having the capability of handing off a communication to a second base station as the mobile terminal enters into the second base station's service area or cell. Each base station is allocated a set of numerous frequency pairs (voice channels), each pair to allow duplex operation, to allow simultaneous separate service of numerous mobile terminals. Control functions are generally communicated over a single control channel for a given cell. These include requests and acknowledgments from and to mobile terminals for call set-ups. Different voice and control channels are used as between adjacent cells. Typically, the base stations use one transceiver per channel, with the first transceiver on a rack being the one dedicated to the cell's control channel.

In normal cellular telephone operation, the base station is connected by wire line to a central switching complex, known as a "mobile telephone switching office," at which all call routing functions, including handing off, typically are performed. Thus, for example, a mobile terminal call addressed to another mobile terminal, even within the same cell, is directed by the base station to the mobile telephone switching office for routing back to the base station for connection with the addressee terminal.

There are situations in which normal cellular operation including the above-mentioned features is not available or even appropriate. As examples, thinly populated and traveled areas and radio isolated areas such as underground garages generally are not appropriate for full cellular service by expensive full-function base stations and digital switching equipment. Nonetheless, given the large number of cellular mobile terminals now in use, and, in many cases, installed in automobiles, it clearly would be a valuable extension of service of the mobile terminals to allow their use in situations in which full cellular service is not available.

In summary, the invention provides an economical means for connecting a cellular mobile terminal to a wire line by employing a limited-function base station comprising a central processing unit and one or more transceivers capable of communicating on and switching between voice and control channels used in full cellular operation. The use of dual function transceivers affords the additional advantages of reducing the number of transmitters required in a base station, allowing a minimum configuration of a single transceiver, and, in the case of a multi-transceiver base station, allowing continued operation even if the transceiver dedicated to the control channel fails.

As a "stand-alone" base station, that is, one that performs no handing-off function, the invention is compatible with the installed base of cellular mobile terminals and extends their use without the cost of expensive digital switching equipment. With relatively few transceivers and no switching equipment, the base station may be portable. The invention may be implemented in an "originate only" mode or with the paging functions used in normal cellular operation. In terminal-to-terminal (mobile-to-mobile) communication, the invention does not require routing over the wire line to a mobile telephone switching office as required in normal cellular operation.

In order that the invention may be more clearly understood, reference is made to the accompanying drawings which show the preferred embodiment and details of its operation:

FIG. 1 is a block diagram of a preferred embodiment of the base station of the invention;

FIG. 2 is a block diagram of an alternative embodiment of the base station of the invention;

FIG. 3 depicts possible transceiver configurations in the preferred embodiment of the base station of the invention.

FIG. 1 shows an embodiment of the base station 100 implemented with three transceivers (121, 122, and 123) each switchable from a voice channel to a control channel and back at command, in this implementation, given by central processing unit (CPU) 110. The transmitter outputs of the transceivers (121, 122, and 123) are connected to combiner 131, duplexer 133 and antenna 134 in a known manner, and the receiver inputs of the transceivers (121, 122, and 123) are derived from antenna 134 by means of the duplexer 133 and splitter 132. Base station 100 is implemented with power supply 150 connectable to a standard 110 VAC (or 220 VAC) source and with master oscillator unit 160.

Base station 100 is shown as implemented with transceivers 121 and 122 connected by a four-wire audio link 171 to provide mobile-to-mobile communication on the voice channels used by those transceivers. Transceiver 123 is connected by a four-wire link 172 to a converter 142 for connection by dialer board 141 to a telephone line 173.

These connections are generalized in FIG. 2, which shows an alternative embodiment with base station 200, using audio selector 271 to connect any of transceivers (221, 222, and 223) to each other or to any of telephone line interfaces (241, 242, and 243) to allow any of the transceivers to engage in mobile-to-mobile communications among one another or in mobile-to-land (wire line) communications over wire line 273.

In either embodiment, when the CPU 110 in FIG. 1 or controller 210 in FIG. 2 receives a request from a mobile terminal (not shown) on the control channel, it determines whether to process the call on the basis of factors including whether the call is authorized and whether a requested connection is possible. If the call is to be set up, the CPU or controller transmits over the control channel to the requesting terminal an assignment of a voice channel corresponding to an available transceiver, generally, in the preferred embodiment, the transceiver transmitting the control signals. The CPU or controller then switches that transceiver to its voice channel from the control channel and assigns another available transceiver (not engaged in a conversation) to the control channel.

In the case of mobile-to-mobile communications, the call set-up includes a paging of the addressee terminal and an assignment of a second voice channel to that terminal if acknowledgement is received and communications permitted by the CPU or controller. This would occupy two transceivers, but, unlike normal cellular operation, would not require communication over the wire line. Land-to-mobile communications may be initiated by paging and acknowledgment analogous to normal cellular operation, that is, by transmission of a page and receipt of acknowledgment over the control channel, followed by the assignment of a voice channel.

FIG. 3 shows the possible transceiver states in a three-transceiver implementation of the base station of the invention. When all the transceivers are in active voice state, the system is busy and mobile originations are not possible because there is no control channel open. When one of the calls is terminated, the base station transceiver that has been released will switch back to an active control state. Thus, whenever possible, there will be one control channel open.

The above are illustrative embodiments of the invention. As few as one transceiver may be used in the base station, or as many transceivers as allowed by frequency allocations.